So it may come as something of a surprise to be reminded that as much fun as StarCraft 2: Wings of Liberty was, you've got two more campaigns coming your way. At a recent press event inside Blizzard HQ in Irvine, California, we got to take a look at two single-player missions from Heart of the Swarm, the first expansion pack-priced followup, focused on the popular Zerg race.

One note of warning before we begin: There are story elements revealed in these missions that will sorta, kinda spoil the plot of Wings of Liberty if you haven't finished it yet. If you aren't done with Jim Raynor's Terran campaign, play that and then come back. Otherwise, feel free to read on.

Gallery: StarCraft 2: Heart of the Swarm (5/31/2011) | 40 Photos

Last time we saw Kerrigan, she was looking a little more human and a little less Queen of Blades than when she started the Terran campaign. But the two missions Blizzard showed us had her back among the Zerg (in Terran form "with these Zerg dreadlocks," jokes lead writer Brian Kindregan), commanding her units with power. What exactly happened?

"She as a human was always a very powerful psionic," he says, but controlling the zerg outside of the Queen of Blades form is a new trick. "So clearly, not all is as it seems. You find yourself early on in the game running around trying to regain control of the Swarm. Why she's doing that is a big question that will be answered as people play the game."

The first mission takes place on the planet Char, a globe already ravaged by Zerg and then Terran forces. A rogue broodmother named Za'gara has pulled together some forces of her own, and it's up to Kerrigan and her troops to show her who's boss.

That's a new angle on the alien race, says Kindregan. "The Zerg are generally percieved as this single entity hivemind, and they've actually always have had subcommanders who are individually sentinent that bow to the greater force, whether that's Overmind or the Queen of Blades. But that has never been explored very deeply, and now this is our chance to explore the day-to-day life of Zerg and what kinds of schisms might develop."

To fight Za'gara, Kerrigan is tasked with collecting 100 eggs on the map before her foe does, and the level not only teaches how to balance expeditionary attacks (there are a few "strongholds" of eggs, each with their own "Feral Zerg" creep forces of various strengths to clear out) with base defense. The level also introduces the suicidal exploding Baneling by dishing out a few units at a time to experiment with, and (once Kerrigan gathers all the necessary eggs before her opponent) a huge army of the new unit to use in one grand attack against the rogue leader.

While you play, Kerrigan serves as a sort of unique hero unit -- she has various abilities that spend energy, and will respawn within a few minutes if killed. But don't expect Heart of the Swarm to bring back Warcraft 3's popular hero system; Kerrigan's one of a kind.

"We're really trying to embrace the concept of Kerrigan as a goddess of the Zerg," says production director Chris Sigaty. "This is really something to enhance Kerrigan as a powerful being -- she can take a siege tank blast. She is a true hero."

Eventually, of course (if the player's successful), Kerrigan gets the eggs and demolishes the Zerg base. But she ends up saving the life of her traitorous broodmother. By winning the battle, Kerrigan proves to Za'gara that she's worthy of leading the Zerg, and seemingly earns her loyalty back.

In between missions, Kerrigan will travel the universe from inside her Leviathan, and the layout there is a little simpler than Raynor's Hyperion ship. There's a wide open window in the front that allows you to clearly see what planet you're on in living color, and Kerrigan's flanked by two assistants. One, Abathar, is the Zerg evolution master, and he oversees the evolution of all your units. The other, Izsha, is listed only as an advisor, but she tells Kerrigan early on that she's the embodiment of the Queen of Blades persona, and Kerrigan's link back to controlling the Zerg. She serves as communications, mostly, informing the player of missions and tactics on the ground.

Abathar's chamber is the equivalent of Raynor's armory, though the Zerg runs things a little differently. During missions you can collect mutagen units, which can then be used to not only add new functions to various zerg units, but even mutate them into entirely different forms. Zerglings, for example, can get upgraded to move faster or spawn instantly, but they can also be evolved into Swarmlings (which spawn three at a time instead of two) or Raptors (which have a health bonus and can leap into battle). Roaches can be upgraded into either Prowlers and move around while burrowed or Leeches, with a bonus to life and faster regen underground.

Of course, all of those bonuses are still being worked on, but it's all part of "the core concepts of the Zerg in general," says Sigaty. "You're creating the army you want in a much more evolving sense than you saw in Wings of Liberty." Kerrigan also evolves -- she has a few different specializations that each come with their own abilities (I saw two called Spec Ops and Corruption in action, but were told there might be up to six to play with in the finished game).

The second mission takes place on a new planet called Kaldir, and Kindregan says there was a very simple origin for this one. "That mission started with a pretty simple idea, as often happens," he says. "Everybody kind of wanted to go to an ice planet."

Yes, Kaldir is an ice planet, where frozen storms whip across the surface and neutral yeti monsters attack in raids. Here Kerrigan is looking for another lost Zerg brood called the Na'fash, but when she arrives, she finds two different threats instead. First, Kaldir suffers from storms that cause a condition called flash freeze -- periodically, winds will come up and freeze your units in place temporarily, keeping them from moving or attacking.

Fortunately, there's a quick solution to this problem -- Kerrigan can defeat the local yeti, grab their DNA, and after a few kills, Abathar can upgrade all Zerg to make them immune to the flash freeze. As soon as that happens, however, Kerrigan encounters another threat: The Protoss have landed on Kaldir, and she has to move quickly to try and take down three communications spires that they'd use to report her position.

There's one more discovery, however: While flash freeze starts off the mission as a liability, it grows into an advantage for Kerrigan. Properly evolved, her Zerg are immune to the condition, but the Protoss are not, allowing you to plan your attacks against a frozen and helpless foe. "You can start to get, 'Oh wow I can time my pushes with this,'" says Sigaty. "It's simple. But it does add to how you play on that mission. And that sort of thing is what we want to hit."

"It's such a Zerg-y thing," says Kindregan, "that you go to a place that's incredibly hostile and can do terrible things to you, and you find that DNA or that mutagen or whatever it is that lets you evolve and adapt and survive it. So that really became the early part of the mission, about changing the swarm to be able to live on that planet, as opposed to trying to change the planet, which is what humans or Protoss would do."

We didn't see any multiplayer this time around, and while Sigaty said that of course there'd be new units and strategies there to play with, Blizzard doesn't want to break what's not broken. "We're in a very good place," he says. "But there is too much of a good thing when it comes to StarCraft 2. Going much beyond Brood War doesn't necessarily make for a better game, it makes for more options that end up making it more confusing, losing a lot of that chesslike aspect. So it's a very fine line for us to walk here."

And looking past Heart of the Swarm, Kindregan confirms that there will be some story hooks to the final chapter of the StarCraft 2 trilogy, though not before some big StarCraft lore is revealed. "The deeper story of the StarCraft universe really has its seeds back in the original campaign," he says. "There's forces at work in the background, and in Heart of the Swarm, some of those story elements and forces are going to actually come to the fore, so that story is going to have a lot more visibility than it has in the past."

"It is a complete story of Sarah Kerrigan and the Zerg," he continues, making it clear that the Heart of the Swarm campaign will stand on its own as Wings of Liberty did. But keep your eyes open, because there's more to come. "As the overall story progresses, as they tend to do with Blizzard products, things are going to get more and more epic. And for something to really have that epic quality, I think you have to feel like it's been seeded and set up and developed and growing rather than just pulling a curtain aside and saying look, epicness! We definitely want Heart of the Swarm to have its own satisfying ending."